Virgo Meteor Sky View
Some hints for what it is for and how to use it
Italiano
The Virgo JAVA applet doesn't start!

What is Virgo?
Virgo's data source
Daytime radio meteor showers
The sky view display
Aren't east and west mixed up?
The azimuth indicator
Adding your call and locator
Let Virgo remember you
That scatterbrained Virgo doesn't remember my data!
OSWIN 53 MHz RADAR data
If you are no radio amateur or short wave listener
Basics to read

Meteor related topics
What is this Antihelion Source?

If you have additional questions
What is Virgo?
Virgo is a projection of the sky visible at your location. Different to other astronomical sky views, there are no stars displayed, but the radiants of current meteor showers. Virgo uses the drift corrected data of the International Meteor Organization to give you a view of the meteor sky above you, updated minute by minute.

Virgo is originally designed to serve for meteorscatter propagation purposes in amateur radio.

You can easily adopt Virgo for other purposes if you just read the hints for non-ham users.

The Virgo JAVA applet does not start
Since JAVA version 7, there might be problems starting Virgo with JAVA throwing an AccessControlException error. JAVA considers all http links as potentially unsecure now, so you have to tell it explicitely which "unsecure" websites you want to accept. Please read the JAVA website for hints:
How to add Virgo to your exception list

According to my own experience, you have to add "http://dl1dbc.net" and "http://www.dl1dbc.net". Richard, KB7IJ, and Roger, VE1SKY, recently confirmed this procedure to be successful.

Several users found it's not enough to add the URLs to the JAVA exception list to get the applet running.

The final solution is to add two lines to the file "java.policy". You'll find it under the JAVA installation directory usually C:\Program Files\Java\jre1.8.0_45\lib\security
Add them into the section "grant" as follows:

grant {
...
permission java.net.SocketPermission "dl1dbc.net:80", "connect";
permission java.net.SocketPermission "dl1dbc.net:80", "resolve";
...
}

As an example, have a look into this java.policy file.

This valuable recipe comes to you from Ladislav, OK1DIX, and was confirmed working by Jozsef, HA1VQ.

Thanks a million, Ladislav and Jozsef!!

Rick, K5GZR, put the steps needed for updating JAVA using the policy tool in a .txt file to remember it. You can download the hints here. Thank you very much, Rick!!

Rodger, G8HLH, told me that this did not work until he used the RESTORE SECURITY PROMPTS button. So check this out, too.

Marek, SP2MKO, and Nick, UX4UA, found problems using Google's Chrome browser. So always try another browser before giving up!

Milan, OK1DMP, gives hints when using Windows 10:
1. Google chrome is a problem because old NPAPI applets (including Java) are not supported any more - Chrome will not work definitely.
2. Windows 10 introduce a new Internet browser - Microsoft Edge which didn't work too - the web page shows a message: "If you don't see the meteor sky view applet, please scroll down this page for hints..."
3. Using setup ("..." upper right) there is an option "Open by Internet Explorer..." and voila - it works ! You have to allow run a java program. Assume using Java Control Panel - Security all "dl1dbc.net" exceptions were added to Exception Site List.

Finally, Jozsef, HA1VQ, tried Firefox ESR (Extended Support Release) with great success! Please don't forget all the entries in the exception list and the "Java Policy" file mentioned before. Have fun!

Virgo's data source
Starting in 1995, the International Meteor Organization (IMO) publishes celestial and activity data for meteor showers which produce definite visual or radio activity. Right ascension (RA) and declination are the astronomical coordinates that, transformed to our own geocentric view of the world, give azimuth and elevation for each point in time the meteor radiant moves through our visible sky. The activity data tell us, in which period of the year the specific meteor shower is active, when it reaches its maximum and what zenithal hourly rate the shower produces throughout its peak. The IMO is definitely not the only organization providing this data, but this data source has one advantage over others, offering a table with information about the drift positions of the meteor showers' radiants.

Virgo uses drift corrected celestial data by inter- or extrapolating the given data from the IMO for each day of observation.

Daytime radio meteor showers
Note that most of the information provided by the meteor organizations is meant for visual observers. So any peak ocurrence of a meteor stream at daytime makes it a radio meteor shower listed in table 7 of the IMO meteor calendar. The table lacks of radiant drift positions following in an inaccurate depiction of the sky view for dates far from the peak time.

Virgo assumes a drift in right ascension (RA) of 1 degree per day, reducing the activity time of each daytime meteor shower on 10 days before and after the given maximum. Note that the declination is not drift corrected being of lower importance for directing your antenna.

The intensity of the meteor showers when peaking is given in the terms "low, medium, high". Virgo assigns the activity to the following AMS classes:

low class 4
medium class 2
high class 1

The sky view display
This is the big blue target with lots of cyan colored dots traversing it. The center of the sky view display is where you are - if you have entered your location correctly. So if you are located at the center of the sky view, the outer rim of the blue area marks your visible horizon. Meteor radiants that travel over the blue field can be used for meteorscatter, radiants below your horizon are out of sight for your antenna.

The radiant's path is represented by an arc of cyan colored dots. Each of this dots marks an angle of 7.5 degrees or half an hour travel time of the corresponding meteor radiant.

The radiant itself is marked by a big colored dot with the short reference near to it. Using Virgo, you will find orange dots for meteor showers that issue up to three meteors per hour at maximum, red dots for meteor showers with up to ten meteors per hour. You should be alerted, when a radiant is marked in magenta. Those meteor showers provide at least 60 specimen per hour or one meteor per minute when they reach their visual activity peak.

You can easily track the radiant's path over your visible sky. Concentric lines show you the elevation over ground the radiant passes by at the moment. In the example shown, the Orionids (ORI) radiant is positioned at a moderate elevation of about 53 degrees, while the meteors from the Delta-Aurigids radiant hit your skull nearly from the zenith (at about 88 degrees elevation).


Aren't east and west mixed up?
No! Astronomical sky views are always oriented with east and west in reverse order. If you are not a radio amateur but a mentally healthy human being, you will take the sky view out of the house, hold it over your head and look for the meteors. In this orientation, east and west are in the right place!

A Swiss radio amateur (HB9DFG) told me that he is not used to go out and hold his monitor over his head. So Virgo got another checkbox in her sky display control section where you can switch the orientation of East and West.

With the Ticks and Labels checkboxes you can choose, whether the radiant's path is displayed and whether the short reference of the meteor shower is added near the radiant's symbol. In cases where many minor showers are active, the interfering lines and labels may be puzzling.

The azimuth indicator
Meteors approaching from a distinct radiation point (the meteor shower's radiant) cross the the Earth's atmosphere on parallel trails. If you want to be sure to get at least one in a position for which the scatter law is fulfilled, your antenna should be oriented nearly perpendicular to the meteors' trails (trail efficiency) [3]. The azimuth indicator shows the preferred antenna directions for each given meteor shower by default.

You can surely receive a higher signal strength and longer ping duration if the propagation path is about parallel to the meteor's ionisation trail [2]. But pointing your antenna parallel to the meteor swarm will lower your chance that your rf will be scattered at all.

Depending on what you choose from the azimuth indicator's controls, the azimuth indicator will show you the preferred antenna direction or the path orientation of the meteors dipping into the atmosphere. All pointers are colored corresponding to the meteor shower they represent. You are free to choose your antenna's orientation somewhere between the meteor's path and the preferred antenna direction. Maybe you just ignore the azimuth indicator.

Adding your call and locator
It is very important, that you first enter your locator before using Virgo. On start-up, call and locator input fields are initialized with "DL1DBC" and "JO31oj". So if you don't live next to me by chance, you should enter your locator to get your sky and not mine. Click the "GO" button to update the display.

If you are no radio amateur or short wave listener, please read the additional hints.


Let Virgo remember you
On start-up, Virgo tries to set a cookie. If your browser accepts permanent cookies, you can store your data in Virgo's database through activating the "Save Data" checkbox before pressing the "GO" button. Please read the following note:

That scatterbrained Virgo doesn't remember my data!
It is not quite easy to set and get a cookie from within a JAVA applet. I won't bore you with the details. With some browsers or operating systems there are problems getting the cookie back to the server. In this case, you have to close the browser, start it again and repeat the saving procedure.

If Virgo permanently refuses to store the data anyway, please check whether a cookie could have been set by the server (its name is "virgo"). Maybe your browser is not allowed to accept permanent cookies.

OSWIN 53 MHz RADAR data
The Leibniz Institute of Atmospheric Physics e.V. at University of Rostock in Kühlungsborn (IAP Kühlungsborn) close to the shore of the Baltic Sea maintains the VHF Ostsee Wind Radar OSWIN. The institute kindly granted permission to use the backscatter data given by the meteor detection sky map for information of the amateur radio community.

Please note: All results are provided for information only and must be validated by the issuing authority (IAP Kühlungsborn) before use.

The OSWIN sky display
Within the Virgo display, there is a little sky display in the OSWIN section. This sky display is centered on JO54vc, the position of the RADAR at the Baltic Sea. According to Virgo's big sky display that shows your own sky, the little one displays the meteor sky as seen by OSWIN. In the example depicted to the right, the radiant of a class 0 meteor shower (magenta colored dot) is in OSWIN's focus.

Please note that the OSWIN's meteor sky may differ enormously from your own sky view. Low backscatter rates from OSWIN may be the result of the expected meteor shower being under OSWIN's horizon!

The OSWIN data chart
Meteor backscatter data are provided from IAP Kühlungsborn every ten minutes summarized over one hour detection time. Although Virgo displays only 24 datasets for every day in its bar graph (see yellow colored bars in the figure below), the ten minutes update is shown as well. In the figure below you can see a cyan colored bar representing the ten minutes data update. The recent number of meteor events during one hour detected by the OSWIN RADAR is displayed numerically near to the right border of the chart.

With the help of Virgo's bar chart you can easily track the daily variation of meteor activity which is highest around six o'clock local time when the sky is sort of windshield in the motion direction of the earth. The seven days display allows you to estimate the raising meteor activity due to a meteor shower on the way towards its maximum.

Please note, that even when working on six meters (the operating frequency of the OSWIN RADAR) there are clear differences between the number of meteors detected by backscatter and possible forward scatter events. Don't expect to hear 91 pings when OSWIN does!

Data acquistion is done by an independent client requesting data shortly after update of the source. Expect Virgo's bar chart and the meteor events number to be updated one or two minutes after you recognize a change on the OSWIN website. Due to high traffic load onto IAP's server during special meteor events, data acquisition can be delayed while the client is still trying to connect or even be cancelled after timeout. In rare cases, feeding of the OSWIN data source stops for hours or even for days until the people at the IAP recognize the failure and restart the process. The data gap is detected by the client and marked with magenta colored bars in the chart (see figure above).


Virgo has to go online to gather data from its database every time the OSWIN data chart has to be updated. In the OSWIN control section, you can choose how often Virgo should look for new data. By default, Virgo updates the OSWIN data every ten minutes shortly after acquisition by the retrieving client.

Set to one hour, the update takes place at every full hour. You can even choose none for a fully deactivation of the OSWIN feature.

If you are no radio amateur or short wave listener
It could be worse. The only thing you might bother is passing the coordinates of your location to Virgo. Virgo uses the Maidenhead locator because radio amateurs do so, too. There is a simple way to get this data for your observing location:
  • First change to the web site Heavens above. They maintain a brilliant location database, where you surely can find the place you live in.
  • Once you know your geographical coordinates, switch to AMSAT's conversion dialog. Enter latitude and longitude in the appropriate fields and click the button "Calculate". The value called "gridsquare" is your Maidenhead locator.
  • Enter the Maidenhead locator into Virgo's input field "Your locator" and click the "GO" button. And done!
Instead of an amateur radio or short wave listener call sign just enter your name or a special location into Virgo's input field "Your call sign".

Basics to read
If you are new to meteorscatter, please try to read some basic articles:
  1. The International Meteor Organization: Theory of Meteor Reflection
  2. James Richardson, The American Meteor Society: Some Notes and Equations for Forward Scatter
  3. OH5IY: Meteors and Communication, part 2; Chapter Forward Scatter Geometry ff.
If you have additional questions
...don't hesitate to send me an email:

sabine+++dl1dbc.net (please replace +++ by the at character)

73
Sabine, DL1DBC